Description

Sheltered to extremely sheltered mid eulittoral pebbles and cobbles lying on sediment subject to variable salinity and characterized by the wrack Fucus vesiculosus. The wrack Ascophyllum nodosum can occasionally be found on larger boulders, while the barnacles Semibalanus balanoides and Elminius modestus and the mussel Mytilus edulis can be present on cobbles. Winkles, particularly Littorina littorea, commonly graze on the seaweeds, while Littorina saxatilis can be found in crevices. Ephemeral seaweeds such as Ulva intestinalis can occupy available space. There is likely to be some variation in the ephemeral seaweeds and their abundance depending on the season. Patches of sediment found between the hard substrata often contains the lugworm Arenicola marina or the sand mason Lanice conchilega, while the crab Carcinus maenas, gammarids and amphipods occur on and under cobbles (see Connor et al., 2004).

Depth range

Upper shore, Mid shore, Lower shore

Additional information

Fves.VS can be found below the biotope dominated by the wracks Fucus spiralis or Fucus ceranoides (Fspi.X; Fcer) or a community dominated by Semibalanus balanoides, Patella vulgata and Littorina littorea (BLitX). It is found above a community dominated by Mytilus edulis (Myt.Myt) or the wrack Fucus serratus (Fserr.VS).

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Further information sources

Sensitivity characteristics of the habitat and relevant characteristic species

This biotope is characterized by a canopy of Fucus vesiculosus which can be found attached to suitable substrates. Other macroalgaes found on the shore include Ascophyllum nodosum which can be found attached to larger boulders. The native barnacle Semibalanus balanoides and the invasive non-native species Elminius modestus and the mussel Mytillus edulis are found on boulders and cobbles, but are not considered to be a key characterizing speices. Littorinids are the dominant faunal grazers within this biotope. In the finer sediments Arenicola marina and Lanice conchilega can be present. The main predator found on the shore is the crab Carcinus maenus.

Fucus vesiculosus is the key structuring species of this biotope. The macroalgae forms a canopy that provides protection from desiccation for underlying fauna. The macroalgae forms a canopy that provides protection from desiccation for the various underlying species and for a range of epifauna on the fronds themselves. As ecosystem engineers fucoid algal canopies modify habitat conditions. This can facilitate the existence and survival of other intertidal species and therefore strongly influencing the structure and functioning of intertidal ecosystems (Jenkins et al., 2008).

Resilience and recovery rates of habitat

Since the 1940s major declines in the distribution of Fucus vesiculosus (Kautsky et al., 1986) and even local extinctions (Nilsson et al., 2005) have been observed in the Baltic Sea where the species dominates the shallow hard-bottom areas. The decline is likely a consequence of increased anthropogenic stress. Large-scale disappearance of Fucus vesiculosus from an ecosystem can result in changes in the community composition (Wikstrom & Kautsky, 2007). The canopy created by Fucus vesiculosus forms a microclimate for the understory fauna and flora. Removal of the canopy exposes under lying fauna and flora to environmental conditions with which they would be intolerant of resulting in mortality events.

Fucus vesiculosus recruits readily to cleared areas of the shore and full recovery takes 1-3 years in British waters (Hartnoll & Hawkins, 1985). Keser & Larson (1984) investigated the recovery of Fucus vesiculosus to plots which had been scraped clean and burned with a propane torch. Fucus vesiculosus was the first perennial alga to colonize the experimentally denuded transects, even at sites and tidal levels that had been dominated by Ascophyllum or Chondrus beforehand. Recovery occurred at all sites between 3 to 21 months. The study found newly settled germlings of Fucus vesiculosus in most months, indicating a broad period of reproduction. When grazers are excluded from areas of intertidal shores fucoids have the ability to rapidly recolonize areas, they can even be found in areas, which in a balanced ecosystem, they do not normally occur (Burrows & Lodge, 1950, Southward & Southward, 1978). Fucoid distributions return to their recognized zones when grazers are re-established on a shore (Burrows & Lodge, 1950, Southward & Southward, 1978). Although intertidal shores can rapidly regain fucoids it can take considerably longer for ecosystem function to return if grazers have also been lost (Hawkins & Southward, 1992). If the whole community is removed, recovery is likely to occur at a much lower pace. Indeed, Hawkins & Southward (1992) found that, after the M.V. Torrey Canyon oil spill, it took between 10 and 15 years for the Fucus spp. to return to 'normal' levels of spatial and variation in cover on moderately exposed shores. Therefore, for factors which are likely to totally destroy the biotope, recoverability is likely to be low.

Fucus vesiculosus growth rates can vary both spatially and temporally (Lehvo et al., 2001). Temperature, exposure, and light availability are some of the factors which cause these changes in growth rates (Strömgren, 1977, Knight & Parke, 1950, Middelboe et al., 2006). Strömgren (1977) investigated the effect of short-term increases in temperature on the growth rate of Fucus vesiculosus. It was found that the growth rate of the control sample kept at 7°C was 20 times lower than the sample introduced to temperatures of 35°C (Strömgren 1977). When the effect of temperature was investigated on the shore, relative growth rates in summer were found to be as high as 0.7% / day in summer, compared to less than 0.3% / day in winter (Lehvo et al., 2001). For macroalgae the trend is for shorter individuals in situations with greater wave exposure (Lewis, 1961, Stephenson & Stephenson, 1972, Hawkins et al., 1992, Jonsson et al., 2006). Fucus vesiculosus also comply with this trend, and growth rates mirror this difference in physiology. On Sgeir Bhuidhe, an exposed shore in Scotland, Fucus vesiculosus grew on average 0.31 cm / week. On a sheltered Scottish shore the average increased to 0.68 cm / week (Knight & Parke, 1950).

The development of the receptacles takes three months from initiation until when gametes are released (Knight, 1947). On British shores, receptacles are initiated around December and may be present until late summer (Knight , 1947). The alga is dioecious, and gametes are generally released into the seawater under calm conditions (Mann, 1972; Serrão et al., 2000) and the eggs are fertilized externally to produce a zygote. Serrão et al. (1997) determined that the wrack had a short-range dispersal capacity. Under calm conditions in which eggs are released, most eggs fall in the immediate vicinity of the parent plants. The egg becomes attached to the rock within a few hours of settlement and adhere firmly enough to resist removal by the next returning tide and germling may be visible to the naked eye within a couple of weeks (Knight & Parke, 1950). Despite the poor long range dispersal, the species is highly fecund often bearing more than 1000 receptacles on each plant, which may produce in excess of one million eggs. On the coast of Maine, sampling on three separate occasions during the reproductive season revealed 100% fertilization on both exposed and sheltered shores (Serrão et al., 2000). Fertilization is thus not considered as a limiting factor in reproduction in this species (Serrão et al., 2000).

Mortality is extremely high in the early stages of germination up to a time when plants are 3 cm in length and this is due mostly to mollusc predation (Knight & Parke 1950). While Fucus vesiculosus may resist some degree of environmental stress, their long-term persistence depends on their reproductive ability as well as the survival and growth of early life history stages (germlings) that are generally more susceptible to natural and anthropogenic stressors than adults (Steen, 2004; Fredersdorf et al., 2009). It is therefore necessary to include early life stage responses in the assessment of effects of environmental changes on fucoid algae as only considering fully developed adults specimens may lead to false conclusions (Nielsen et al., 2014).

Genetic diversity can influence the resilience of fucoids in particular when pressure persists over a long period of time. Genetically diverse populations are generally more resilient to changes in environmental conditions compared to genetically conserved populations. Tatarenkov et al. (2007) determined a high level of genetic variation in Fucus vesiculosus and extensive phenotypic variations. This could explain why the species is more successful than most fucoid species in colonizing marginal marine environments such as low-salinity estuaries, showing a range of morphological, physiological and ecological adaptations (Tatarenkov et al. 2005). Pressures causing a rapid change will have a greater impact as the natural ability of the species to adapt is compromised.

In addition to sexual reproduction, Fucus vesiculosus is also able to generate vegetative regrowth in response to wounding. McCook & Chapman (1992) experimentally damaged Fucus vesiculosus holdfasts to test the ability of the wrack to regenerate. The study found that vegetative sprouting of Fucus vesiculosus holdfasts made a significant addition to the regrowth of the canopy, even when holdfasts were cut to less than 2 mm tissue thickness. Four months after cutting, sprouts ranged from microscopic buds to shoots about 10 cm long with mature shoots widespread after 12 months. Vegetative regrowth in response to wounding has been suggested as an important mean of recovery from population losses (McLachan & Chen, 1972). The importance of regeneration will depend on the severity of damage, not only in terms of the individuals but also in terms of the scale of canopy removal (McLachan & Chen, 1972).

Resilience assessment. If specimens of Fucus vesiculosus remain in small quantities it is likely that re-growth will occur rapidly due to efficient fertilization rates and recruitment over short distances. The ability of Fucus vesiculosus to re-grow from damaged holdfasts will also aid in recolonization. Recovery is likely to occur within two years resulting in a ‘High’ resilience score. However, if the population is removed (resistance is ‘None’) , recovery may take longer, perhaps up to 10 years (as seen after the M.V. Torrey Canyon oil spill) so the resilience would be scored as ‘Medium’.

The resilience and the ability to recover from human induced pressures is a combination of the environmental conditions of the site, the frequency (repeated disturbances versus a one-off event) and the intensity of the disturbance. Recovery of impacted populations will always be mediated by stochastic events and processes acting over different scales including, but not limited to, local habitat conditions, further impacts and processes such as larval-supply and recruitment between populations. Full recovery is defined as the return to the state of the habitat that existed prior to impact. This does not necessarily mean that every component species has returned to its prior condition, abundance or extent but that the relevant functional components are present and the habitat is structurally and functionally recognisable as the initial habitat of interest. It should be noted that the recovery rates are only indicative of the recovery potential.

Hydrological Pressures

In the north east Atlantic Fucus vesiculosus occurs from Northern Russia to Morocco (Powell, 1963). Within this range Fucus vesiculosus can survive in a wide variety of temperatures. Fucus vesiculosus is able to tolerate temperatures as high as 30 °C (Lüning,1990) and did not show any sign of damage during the extremely hot UK summer of 1983, when average temperatures were 8 °C hotter than normal (Hawkins & Hartnoll, 1985). Fucus vesiculosus also tolerates extended periods of freezing in the northern part of its range.

Sensitivity assessment. Both Fucus spiralis and Fucus vesiculosus are found in the middle of their natural temperature range in the British Isles and will therefore not be affected by an increase in 5 °C for one month or an increase of 2 °C for one year. Both resistance and resilience are thus assessed as ‘High’ (no impact to recover from). The biotope is ‘Not Sensitive’ to this pressure at the pressure benchmark.

In the north east Atlantic Fucus vesiculosus occurs from Northern Russia to Morocco (Powell, 1963). Within this range Fucus vesiculosus can survive in a wide variety of temperatures. Fucus vesiculosus is able to tolerate temperatures as high as 30 °C (Lüning,1990) and did not show any sign of damage during the extremely hot UK summer of 1983, when average temperatures were 8 °C hotter than normal (Hawkins & Hartnoll, 1985). Fucus vesiculosus also tolerates extended periods of freezing in the northern part of its range.

Sensitivity assessment. Both Fucus spiralis and Fucus vesiculosus are found in the middle of their natural temperature range in the British Isles and will therefore not be affected by a decrease in 5 °C for one month or a decrease of 2 °C for one year. Both resistance and resilience are thus assessed as ‘High’ (no impact to recover from). The biotope is ‘Not Sensitive’ to this pressure at the pressure benchmark.

Fucus vesiculosus is well adapted to cope with varying salinities and can grow in full saline to brackish conditions. Indeed Fucus vesiculosus is the dominant large perennial seaweed in the Baltic Sea growing in salinities down to 4 psu (Kautsky, 1992). Bäck et al. (1992) compared Fucus vesiculosus individuals from Atlantic and the Baltic populations. Both populations were able to withstand wide range of salinities in laboratory cultures, yet some differences were recorded. The Atlantic population showed better growth in higher salinities and virtually no growth at 5 ppt. Those individuals kept at 5 ppt mortality occurred after 7 weeks. In contrast the Baltic wracks grew better in conditions with lower salinities. Growth was negligible at the highest tested salinity (45 ppt). Back et al., (1992) demonstrate that sensitivity of Fucus vesiculosus to changes in salinity differ between populations.

Serrao et al. (1996a) found that lower salinities can negatively affect both the fertilization rates and recruitment success of Fucus vesiculosus. Serrao et al. (1996a) also concluded that the osmotic tolerances of Fucus vesiculosus gametes limit the species distribution in the Baltic Sea. These studies show that low salinities limit the recruitment and fertilization success of fucoids. There is also evidence suggesting that reduced salinities can influence the rate of receptacle maturation in fucoids (Munda, 1964). Rate of fructification in both Ascophylum nodosum and Fucus vesiculosus has been measured to increase in diluted seawater (Munda, 1964).

Sensitivity assessment. An increase in salinity for this biotope would mean salinity levels would become hyper-saline. Fucus vesiculosus is not adapted for these conditions and a change in this pressure at this benchmark would cause some mortality. Other species within this biotope may be able to tolerate an increase in salinity, however the loss of Fucus vesiculosus would lead to a change in the biotope. Both resistance and resilience are thus assessed as ‘Medium’. The biotope has a ‘Medium’ sensitivity to this pressure at the pressure benchmark.

Fucus vesiculosus is well adapted to cope with varying salinities and can grow in full saline to brackish conditions. Indeed Fucus vesiculosus is the dominant large perennial seaweed in the Baltic Sea growing in salinities down to 4 psu (Kautsky, 1992). Bäck et al. (1992) compared Fucus vesiculosus individuals from Atlantic and the Baltic populations. Both populations were able to withstand wide range of salinities in laboratory cultures, yet some differences were recorded. The Atlantic population showed better growth in higher salinities and virtually no growth at 5 ppt. Those individuals kept at 5 ppt mortality occurred after 7 weeks. In contrast the Baltic wracks grew better in conditions with lower salinities. Growth was negligible at the highest tested salinity (45 ppt). Back et al., (1992) demonstrate that sensitivity of Fucus vesiculosus to changes in salinity differ between populations.

Serrao et al. (1996a) found that lower salinities can negatively affect both the fertilization rates and recruitment success of Fucus vesiculosus. The critical limit for recruitment of Fucus serratus in the Baltic Sea is 7 psu (Malm et al., (2001). Serrao et al. (1996a) also concluded that the osmotic tolerances of Fucus vesiculosus gametes limit the species distribution in the Baltic Sea. These studies show that low salinities limit the recruitment and fertilization success of fucoids. However, there is also some evidence suggesting that reduced salinities can influence the rate of receptacle maturation in fucoids (Munda, 1964). Rate of fructification in both Ascophylum nodosum and Fucus vesiculosus has been measured to increase in diluted seawater (Munda, 1964).

Sensitivity assessment. Although a decrease in salinity scale may not cause extensive mortality in Fucus vesiculosus it may affect the reproduction and recruitment success and cause a decrease in the density of the population. A further decrease in salinity also has the potential to reduce the species biodiversity on the shore. Both resistance and resilience are thus assessed as ‘Medium’. The biotope has ‘Medium’ sensitivity to this pressure at the benchmark.

Water motion is a key determinant of marine macroalgal production, directly or indirectly influencing physiological rates and community structure (Hurd, 2000). Higher water flow rates increase mechanical stress on macroalgae by increasing drag. This can result in individuals being torn off the substratum. Once removed, the attachment cannot be reformed causing the death of the algae. Any sessile organism attached to the algae will also be lost. Fucoids are however highly flexible and are able to re-orientate their position in the water column to become more streamlined. This ability allows fucoids to reduce the relative velocity between algae and the surrounding water, thereby reducing drag and lift (Denny et al., 1998).

Jonsson et al. (2006) found that flow speed of 7-8 m/s completely dislodged Fucus vesiculosus individuals larger than 10 cm. Smaller individuals are likely to better withstand increased water flow as they experience less drag. The risk of dislodgement is greater where algae are attached to pebbles instead of bedrock. Indeed if sediment type is small and the substratum is less stable, individuals may eventually reach a critical size when the drag force exceeds gravity and the plant will be moved together with its substratum (Malm, 1999). This risk is increased during the late phase of reproduction when Fucus vesiculosus receptacles become swollen and gas-filled increasing the uplifting force of water flow (Isaeus, 2004).

Propagule dispersal, fertilization, settlement, and recruitment are also influenced by water movement (Pearson & Brawley, 1996). In addition, increased water flow will increase levels of scour which can have a negative impact on small life stages of macroalgae by removing new recruits from the substratum and hence reducing successful recruitment (Devinny & Volse, 1978) (see ‘siltation’ pressures). Changes in water motion can thus strongly influence local distribution patterns of Fucus spp. (Ladah et al., 2008).

On the other hand, a reduction in water flow can cause a thicker boundary layer resulting in lower absorption of nutrients and CO2 by the macroalgae. Slower water movement can also cause oxygen deficiency directly impacting the fitness of algae (Olsenz, 2011).

The water flows experienced by this biotope range from negligible – 0.5 m/s (Connor et al., 2004). An increase in water flow above 0.5 m/s may result in the loss of some fucoid cover. However it must be taken into consideration that almost all of the species found in this biotope, including Fucus vesiculosus, are also found in conditions where the water movement created by wave motion far exceed 0.5 m/s

Sensitivity assessment. An increase in water movement can cause a reduction in fucoid cover due to an increase in the physical stress exerted on them. Reduction in reproduction and recruitment success may also occur. However, at the level of the benchmark a change in water flow is unlikely to have a negative impact on the biotope. Resistance has been recorded as ‘High’ and resilience is recorded as ‘High’ and the biotope is assessed as 'Not sensitive' at the benchmark level.

Emergence regime is a key factor structuring intertidal biotopes. Increased emergence may reduce habitat suitability for the characterizing species. Changes in emergence can lead to; greater exposure to desiccation, reduced levels of time for nutrient uptake and photosynthesising opportunities for the characterizing species.

During the initial stages of drying, when alga are exposed to air, photosynthetic rates increase due to the higher diffusion rate of CO2 in air relative to water (Johnson et al., 1974). However this peak in photosynthesis is usually followed by a gradual decline in the rate of photosynthesis as the surface of the alga dries, thereby preventing further dissolution and uptake of CO2 (Beer & Kautsky 1992). Photosynthesis eventually ceases at a critical state of dehydration when the low water content of the thallus disrupts the functioning of the photosynthetic apparatus (Quadir et al. 1979). Fucus vesiculosus can tolerate desiccation until the water content is reduced to ~ 30%. If desiccation occurs beyond this level, irreversible damage occurs. Individuals at the top of the shore probably live at the upper limit of their physiological tolerance and are therefore likely to be unable to tolerate increased desiccation and would be displaced by more physiologically tolerant species. Tolerance to this pressure is likely to vary on a geographical scale. Gylle et al. (2009) found that Fucus vesiculosus populations naturally occurring in fully saline conditions had a higher emersion stress tolerance compared to brackish populations. Early life history stages are more susceptible to this pressure compared to adults (Henry & Van Alstyne, 2004). Germlings are however protected from desiccation by the canopy of adults. A study by Brawley & Jonhnson (1991) showed that germling survival under adult canopy was close to 100% whereas survival on adjacent bare rock was close to 0% during exposure to aerial conditions. The Fucus canopy is also likely to protect other underlying species to a great extent. Mortalities of other component of the community will however occur if the canopy is removed (see ‘abrasion’ pressure). Fucus spiralis is more tolerant of desiccation stress than Fucus vesiculosus, and is the characterizing species for a very similar biotope to this one which is found further up the shore. An increase in emergence may cause the biotope to change to one more typical of an upper shore location. Alternatively if levels of emergence were to increase then Fucus vesiculosus may be out-competed by a faster growing algae species such as Fucus serratus, an algae species which is found in a number of biotopes which characterize lower shore zones.

Fucoid dominated biotopes are found in the eulittoral zone and are subjected to cyclical immersion and emersion caused by the tides. During the initial stages of drying, when alga are exposed to air, photosynthetic rates increase due to the higher diffusion rate of CO2 in air relative to water (Johnson et al., 1974). However this peak in photosynthesis is usually followed by a gradual decline in the rate of photosynthesis as the surface of the alga dries, thereby preventing further dissolution and uptake of CO2 (Beer & Kautsky 1992). Photosynthesis eventually ceases at a critical state of dehydration when the low water content of the thallus disrupts the functioning of the photosynthetic apparatus (Quadir et al. 1979).

Fucus vesiculosus can tolerate desiccation until the water content is reduced to ~ 30%. If desiccation occurs beyond this level, irreversible damage occurs. Individuals at the top of the shore probably live at the upper limit of their physiological tolerance and are therefore likely to be unable to tolerate increased desiccation and would be displaced by more physiologically tolerant species. Tolerance to this pressure is likely to vary on a geographical scale. Gylle et al. (2009) found that Fucus vesiculosus populations naturally occurring in fully saline conditions had a higher emersion stress tolerance compared to brackish populations.

Early life history stages are more susceptible to this pressure compared to adults (Henry & Van Alstyne, 2004). Germlings are however protected from desiccation by the canopy of adults. A study by Brawley & Jonhnson (1991) showed that germling survival under adult canopy was close to 100% whereas survival on adjacent bare rock was close to 0% during exposure to aerial conditions. The Fucus canopy is also likely to protect other underlying species to a great extent. Mortalities of other component of the community will however occur if the canopy is removed (see ‘abrasion’ pressure).

Sensitivity assessment. Desiccation and the associated osmotic stress, especially when combined with high temperatures can cause mortalities (Pearson et al., 2009). The sensitivity of Fucus vesiculosus to emersion pressure will depend on individual populations as well as the life stage, with germlings being most vulnerable. A change in emergence is likely to cause a change in biotope. Resistance has been assessed as ‘None’ and resilience is assessed as ‘Low’. Overall the biotope has a ‘High’ sensitivity to changes in emergence regime at the pressure benchmark.

The characteristic variable salinity regime of this biotope requires a freshwater influence. The location of this biotope is consequently often near estuaries where marine and freshwater meet. Estuaries are naturally protected areas and have low levels of wave exposure. These two factors are interlinked and create a specific niche within which this biotope is found. As this biotope can be found in extremely sheltered locations, a reduction in wave exposure is unlikely to have any impact on the biological community.

An increase in wave exposure generally leads to a decrease in macroalgae abundance and size (Lewis, 1961, Stephenson & Stephenson, 1972, Hawkins et al., 1992, Jonsson et al., 2006). This biotope is limited to areas with sheltered to very sheltered conditions. Fucoids are highly flexible but not physically robust and an increase in wave exposure can cause mechanical damage, breaking fronds or even dislodging whole algae from the substratum. Fucoids are permanently attached to the substratum and would not be able to re-attach if removed. Organisms living on the fronds and holdfasts will be washed away with the algae whereas free-living community components could find new habitat in surrounding areas. Wave exposure has been shown to limit size of fucoids (Blanchette, 1997) as smaller individuals create less resistance to waves.

As exposure increases the fucoid population will become doiminated by small juvenile algae more resistant to this pressure than mature individuals (Hawkins & Jones, 1992). An increase in wave action beyond this would lead to dominance of the community by grazers and barnacles at the expense of fucoids.

Fucus vesiculosus adapt their morphology to wave exposure to help cope with the stress. Bäck (1993) observed shorter individuals with narrow fronds on exposed shores lacking bladders to reduce drag. An alternative coping strategy for wave induced forces is thallus toughening. In the north and the Baltic Sea, thalli from exposed Fucus vesiculosus were 30% more resistant to tear and breakage compared to conspecifics from more sheltered sites (Nietsch, 2009). Furthermore, Fucus vesiculosus may be better adapted to more exposed positions compared to other fucoids by its ability to regenerate from holdfasts, an ability that Fucus serratus lacks (Malm & Kautsky, 2003).

A change in near shore significant wave height, even where this biotope is found at the upper limit of wave exposure for this biotope, is unlikely to have a significant negative impact. Fucusvesiculosus biotopes found in situations with greater wave exposure such as LR.MLR.BF.FvesB include a greater quantity of barnacles and limpets. However no biotope with variable salinity in greater wave exposure has been described.

Sensitivity assessment. Fucus vesiculosus is sensitive to an increase in wave action. Increased exposure would result in losses of biomass. However the wave exposure and salinity regime found within this biotope are indicative of estuarine conditions and consequently an increase in wave exposure is unlikely. There are also no biotopes with the same salinity regime but with greater wave exposure. As a consequence it is difficult to suggest what biotope may replace this one if an increase in wave exposure was experienced. A decrease in biodiversity may occur. Nevertheless, a 3-5% change in significant wave height (the benchmark) is unlikely to have an adverse affect. Therefore, resistance has been recorded as ‘High’, resilience as ‘High’ and the biotope is assessed as 'Not sensitive' at the benchmark level.

Cole et al. (1999) suggest possible adverse effects on marine species below oxygen levels of 4 mg/l and probable adverse effects below 2 mg/l. Sustained reduction of dissolved oxygen can lead to hypoxic (reduced dissolved oxygen) and anoxic (extremely low or no dissolved oxygen) conditions. Sustained or repeated episodes of reduced dissolved oxygen have the potential to severely degrade an ecosystem (Cole et al., 1999). Reduced oxygen concentrations have been shown to inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012). If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2mg/l (Cole et al., 1999). Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. However, small invertebrate epifauna may be lost, causing a reduction in species richness.

Josefson & Widbom (1988) investigated the response of benthic macro and meiofauna to reduced dissolved oxygen levels in the bottom waters of a fjord. At dissolved oxygen concentrations of 0.21 mg/l, the macrofaunal community was eradicated and was not fully re-established 18 months after the hypoxic event. Meiofauna seemed, however, unaffected by de-oxygenation. Kinne (1970) reported that reduced oxygen concentrations inhibit both algal photosynthesis and respiration.

Sensitivity assessment. The characterizing species Fucus vesiculosus, as well as the other species within this biotope, may be negatively impacted by reduced dissolved oxygen level at the level of the benchmark (2 mg/l for 1 week). A reduction in oxygen levels at the benchmark for this pressure could result in mortalities. The sheltered to extremely sheltered locations where this biotope is are likely to experience lower water mixing (due to wave action and turbulent flow over rocks) than exposed biotopes. However, the biotope occurs in the mid eulittoral and consequently a proportion of time will be spent in the air where oxygen is not limited so the metabolic processes of photosynthesis and respiration can take place. Emergence will mitigate the effects of hypoxic surface waters. Therefore, resistance is assessed as ‘High’. Hence, resilience is assessed as ‘High’, and the biotope as 'Not sensitive'.

The nutrient enrichment of a marine environment leads to organisms no longer being limited by the availability of certain nutrients. The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta-analysis of the effect of contaminants on species richness and evenness in the marine environment. Of the 47 papers reviewed relating to nutrients as a contaminant, over 75% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect. Not all of the 47 papers considered the impact of nutrients on intertidal rocky shores. Yet this finding is still relevant as the meta-analysis revealed that the effect of marine pollutants on species diversity was ‘remarkably consistent’ between habitats (Johnston & Roberts, 2009). It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009). Throughout their investigation, there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant. These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls. However research into the impacts of nutrient enrichment from these sources on intertidal rocky shores often lead to shores lacking species diversity and the domination by algae with fast growth rates (Littler & Murray, 1975; Abou-Aisha et al., 1995; Archambault et al., 2001; Diez et al., 2003; Arévalo et al., 2007).

Major declines of Fucus vesiculosus have been reported from all over the Baltic Sea. These declines have been associated to eutrophication from nutrient enrichment (Kautsky et al., 1986). Nutrient enrichment alters the selective environment by favouring fast growing, ephemeral species such as Ulva lactuca and Ulva intestinalis (Berger et al., 2004, Kraufvelin, 2007). Rohde et al., (2008) found that both free growing filamentous algae and epiphytic microalgae can increase in abundance with nutrient enrichment. This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Berger et al., 2003; Kraufvelin et al., 2007). Nutrient enrichment can also enhance fouling of Fucus fronds by biofilms (Olsenz, 2011). Nutrient enriched environments can not only increase algae abundance but the abundance of grazing species (Kraufvelin, 2007). High nutrient levels may directly inhibit spore settlement and hinder the initial development of Fucus vesiculosus (Bergström et al., 2003).

Changes in community composition on intertidal rocky shores can happen rapidly, and fast growing ephemeral species can become established quickly in the presence of higher concentrations of nutrients. The establishment and growth of these species are not controlled by wave exposure (Kraufvelin, 2007). However, even though these fast growing ephemeral species can become well established quickly, healthy communities on intertidal rocky shores can survive long periods of time, and maintain ecological function after these species have become established (Bokn et al., 2002, 2003; Karez et al., 2004; Kraufvelin et al., 2006b; Kraufvelin, 2007).

Sensitivity assessment. A slight increase in nutrients may enhance growth rates but high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae and an increase in the number of grazers. However, if the biotope is well established and in a healthy state the biotope could have the potential to persist. The effect of an increase in this pressure to the benchmark level should not have a negative impact on the biotope. Therefore the resistance has been assessed as ‘High’. As the resistance is high, as there will be nothing for the biotope to recover from therefore the resilience is also ‘High’. These two rankings give an overall sensitivity of ‘Not Sensitive’.

The organic enrichment of a marine environment at this pressure benchmark leads to organisms no longer being limited by the availability of organic carbon. The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) and decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta-analysis of the effect of contaminants on species richness and evenness in the marine environment. Of the 49 papers reviewed relating to sewage as a contaminant, over 70% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect. Not all of the 49 papers considered the impact of sewage on intertidal rocky shores. Yet this finding is still relevant as the meta-analysis revealed that the effect of marine pollutants on species diversity was ‘remarkably consistent’ between habitats (Johnston & Roberts, 2009). It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009). Throughout their investigation, there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant. These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls. However research into the impacts of organic enrichment from these sources on intertidal rocky shores often lead to shores laScking species diversity and the domination by algae with fast growth rates ( Littler & Murray, 1975; Abou-Aisha et al., 1995; Archambault et al., 2001; Arévalo et al., 2007; Diez et al., 2003).

Major declines of Fucus vesiculosus have been reported from all over the Baltic Sea. These declines have been associated to eutrophication from nutrient enrichment (Kautsky et al., 1986). Nutrient enrichment alters the selective environment by favouring fast growing, ephemeral species such as Ulva lactuca and Ulva intestinalis (Berger et al., 2004, Kraufvelin, 2007). Rohde et al., (2008) found that both free growing filamentous algae and epiphytic microalgae can increase in abundance with nutrient enrichment. This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Berger et al., 2003; Kraufvelin et al., 2007). Nutrient enrichment can also enhance fouling of Fucus fronds by biofilms (Olsenz, 2011). Nutrient enriched environments can not only increase algae abundance but the abundance of grazing species (Kraufvelin, 2007). High nutrient levels may directly inhibit spore settlement and hinder the initial development of Fucus vesiculosus (Bergström et al., 2003). Bellgrove et al. (2010) found that coralline turfs out-competed fucoids at a site associated with organic enrichment caused by an ocean sewage outfall.

Changes in community composition on intertidal rocky shores can happen rapidly, and fast growing ephemeral species can become established quickly in the presence of higher concentrations of nutrients. The establishment and growth of these species are not controlled by wave exposure (Kraufvelin, 2007). However, even though these fast growing ephemeral species can become well established quickly, healthy communities on intertidal rocky shores can survive long periods of time, and maintain ecological function after these species have become established (Bokn et al., 2002, 2003; Karez et al., 2004; Kraufvelin et al., 2006b; Kraufvelin, 2007).

Sensitivity assessment. Little empirical evidence was found to support an assessment of this biotope at this benchmark. The effect of a deposit of 100 gC/m2/yr will have different impacts depending if the deposition was chronic or acute. If the deposition is chronic growth rates may be enhanced and not create any significant negative effects on the biotope. The acute introduction of levels of organic carbon at the benchmark could lead to the overgrowth of the algae by ephemeral green algae and an increase in the number of grazers within a short period of time. Due to the negative impacts that can be experienced with the introduction of excess organic carbon both resistance and resilience have been assessed as ‘Medium’. This gives an overall sensitivity score of ‘Medium’.

Physical Pressures

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’). Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

This biotope occurs on neither sedimentary rock nor soft rock substrata. Any substrate other than the mixed sediment on which this biotope is found would lead to a change in the biotope. Consequently the resistance is assessed as ‘Low’, resilience is Very low (the pressure is a permanent change) and sensitivity is assessed as High. Although no specific evidence is described, confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

This biotope occurs on mixed substrata where the characterizing species, Fucus vesiculosus, and other stable reef species are found on larger sediment fractions. A soft sedimentary habitat or mobile coarse sediment such as gravel or shingle would be unsuitable for these species. Increased sediment instability would also be likely to reduce habitat suitability for littorinids. In sites with mobile cobbles and boulders increased scour results in lower densities of Littorina spp. compared with other, local sites with stable substratum (Carlson et al., 2006). A change to a sedimentary biotope without suitable attachment surfaces would lead to the development of a biological assemblage more typical of the changed conditions.

Sensitivity assessment. A change to a fine or coarse sedimentary habitat would reduce habitat suitability for this biotope, resistance is assessed as ‘None’ and resilience as ‘Very Low’ as the change is considered to be permanent. Sensitivity is therefore assessed as 'High'.

The biological community within this biotope occur either on or within mixed sediment. If the top 30 cm of this biotope were to be removed the biological component of this biotope would have been almost entirely removed. Resistance and resilience are ‘Low’. Sensitivity to this pressure at the benchmark is ‘High’.

This biotope is found on the mid intertidal shore. An area easily accessible by humans especially at low tide. Individual Fucus specimens are very flexible but not physically robust. Fucoids are intolerant of abrasion from human trampling, which has been shown to reduce the cover of seaweeds on a shore (Holt et al., 1997).

Araujo et al. (2009) found that trampling negatively affected Fucus vesiculosus abundance and reduced understorey species, while promoting the colonisation by ephemeral green algae. However, within a year of the disturbance event, Fucus vesiculosus recovered and greatly increased in cover becoming the dominant canopy forming species, replacing a pre-disturbance Ascophyllum nodosum community. The replacement of Ascophyllum nodosum with Fucus vesiculosus may have been due to the poor recovery rate of Ascophyllum nodosum. The increase in abundance suggests the competitive superiority of Fucus vesiculosus individuals in occupying newly available space in the disturbed patches. Similar results were found by Cervin et al. (2005) and Araujo et al. (2012) with Fucus vesiculosus outcompeting Ascophyllum nodosum after small scale disturbances.

Brosnan (1993) investigated the effect of trampling on a number of algal species, including Fucus vesiculosus, on an intertidal rocky shore in Oregon. The effects of 250 tramples per plot, once a month for a year were recorded. Abundances of algae in each plot were reduced from 80% to 35% within a month of the introduction of the pressure, and remained low for the remainder of the experiment.

As few as 20 steps / m2 on stations on an intertidal rocky shore in the north east of England were sufficient to reduce the abundance of fucoids (Fletcher & Frid, 1996). This reduction in the complexity of the algae community in turn reduced the microhabitat available for epiphytic species. Trampling pressure can thus result in an increase in the area of bare rock on the shore (Hill et al., 1998). Chronic trampling can affect community structure with shores becoming dominated by algal turf or crusts (Tyler-Walters, 2005).

Pinn & Rodgers (2005) compared the biological communities found on two intertidal rocky shore ledges in Dorset. They found that the ledge which had a higher number of visitors had few branching algal species, including fucoids, but had greater abundances of crustose and ephemeral species (Pinn & Rodgers, 2005).

The densities of fucoids were recorded from the intertidal rocky shore at Wembury, Devon in 1930 (Colman, 1933) and 1973 (Boalch et al., 1974). Boalch et al. (1974) found a reduction in fucoids on the shore at Wembury and that the average frond length of Ascophyllum nodosum, Fucus vesiculosus and Fucus serratus was smaller.

Fucus vesiculosus is able to generate vegetative regrowth in response to wounding from physical disturbance. McCook & Chapman (1992) experimentally tested the recovery of damaged Fucus vesiculosus. The study found that vegetative sprouting of Fucus vesiculosus holdfasts made a significant addition to the regrowth of the canopy, even when holdfasts were cut to less than 2 mm tissue thickness. Four month after cutting, sprouts ranged from microscopic buds to shoots about 10 cm long with mature shoots widespread after 12 months. Vegetative regrowth in response to wounding has been suggested as an important mean of recovery from population losses (McLachan & Chen, 1972).

Sensitivity assessment. Abrasion of the substratum will cause a reduction in Fucus abundance resulting in ‘Low’ resistance. Several studies however found that the seaweed is able to quickly recolonize disturbed area, out competing other macrolagae such as Ascophyllum nodosum. Although Fucus vesiculosus may return quickly, equilibrium in the ecosystem may not have been reached, therefore resistance is ‘Medium’. Overall the biotope has a ‘Medium’ sensitivity to the pressure.

The mixed substrata found within this biotope can be penetrated, but the impact of this pressure depends on the depth and footprint of the disturbance. There is a lack of evidence to assess the pressure. However sub-surface disturbance will also disrupt the surface layer of this biotope where the majority of the biological community is found. Therefore the assessment for abrasion is the same as that given to the abrasion/disturbance pressure.

Light is an essential resource for all photo-autotrophic organisms and Fucus vesiculosus distribution along a depth gradient strongly correlates with light penetration. In areas with low sedimentation Fucus vesiculosus can survive down to 9-10 m depth (Eriksson & Bergstrom, 2005). Changes in suspended solids affecting water clarity will have a direct impact on the photosynthesising capabilities of Fucus vesiculosus. Irradiance below light compensation point of photosynthetic species can compromise carbon accumulation (Middelboe et al., 2006). Kõuts et al. (2006) found decreases in light intensity in the vicinity of the dredging site resulted in the net decline of Fucus vesiculosus biomass. A decrease in light penetration in the Kiel Fjord caused by an increase in phytoplankton density and shading from filamentous algae has caused an upwards shift of the lower depth limit of Fucus vesiculosus (Rohde et al., 2008).

Increased suspended sediment can also cover the frond surface of Fucus vesiculosus with a layer of sediment further reducing photosynthesis and growth rate. Sediment deposition can also interfere with attachment of microscopic stages of seaweeds reducing recruitment. Berger et al. (2003) demonstrated that both interference with sediment during settlement, and burial after attachment, were significant causes of mortality for Fucus vesiculosus germlings (see ‘siltation’ pressures).

Other characterizing species will also be adversely affected. In particular filter feeding organisms will have their feeding apparatus clogged with suspended particles leading to a reduction in total ingestion and a reduced scope for growth especially since cleaning the feeding apparatus is likely to be energetically expensive.

Sensitivity assessment. Changes in suspended solids reducing water clarity will have adverse effects on the biotope hindering photosynthesis and growth as well as reducing species richness. Resistance is thus assessed as ‘Medium’. Once conditions return to 'normal' algae are likely to rapidly regain photosynthesising capabilities as well as growth rate. Associated communities will also recover as most of the intolerant species produce planktonic larvae and are therefore likely to be able to recolonize quickly from surrounding areas. Resilience is assessed as ‘Medium’. Overall this biotope has a ‘Medium’ sensitivity to this pressure at the given benchmark.

Sedimentation can directly affect assemblages inhabiting rocky shores in different ways, particularly by the burial/smothering and scour/abrasion of organisms. Fucus vesiculosus attaches to the substratum by a holdfast, and is consequently not able to relocate in response to increased sedimentation. Eriksson & Johansson (2003) found that sedimentation had a significant negative effect on the recruitment success of Fucus vesiculosus. Sediment deposition is assumed to reduce macroalgal recruitment by: (1) reducing the amount of substratum available for attachment of propagules; (2) scour, removing attached juveniles and (3) burial, altering the light and/or the chemical micro-environment (Devinny & Volse, 1978, Eriksson & Johansson, 2003). Berger et al. (2003) demonstrated that both interference with sediment during settlement, and burial after attachment, were significant causes of mortality for Fucus vesiculosus germlings.

The state of the tide will determine the extent of impact. If smothering occurs at low tide when the algae is lying flat on the substratum, then most of the organism as well as the associated community will be covered by the deposition of fine material at the level of the benchmark. Smothering will prevent photosynthesis resulting in reduced growth and eventually death. If however smothering occurs whilst the alga is submerged standing upright then the photosynthetic surfaces of adult plants will be left uncovered. The resistance of this biotope to the given pressure may vary with time of day. Germlings however are likely to be smothered and killed in both scenarios and are inherently most susceptible to this pressure. Indeed early life stages are smaller in size than adults and are thus most vulnerable to this pressure as even a small load of added sediment will lead to the complete burial.

Smothering will cause direct mortalities in the associated community, particularly in filter feeding sessile organisms unable to relocate. Low densities of herbivores on rocky shores have frequently been related with areas affected by sedimentation, the presence of herbivores is reduced since their feeding activity and movements might be limited (Airoldi & Hawkins, 2007; Schiel et al., 2006)

This biotope occurs in moderately exposed to very sheltered conditions. In areas with greater water flow or wave action, excess sediments will be removed from the rock surface within a few tidal cycles, reducing the time of exposure to this pressure.

Sensitivity assessment. Burial will lower survival and germination rates of spores and cause some mortality in early life stages of Fucus vesiculosus. Adults are more resistant but will experience a decrease in growth and photosynthetic rates. This pressure will have different impacts on different examples of this biotope depending where on certain environmental gradients they are found. Wave exposure is especially important for this pressure as it is wave energy which will be able to remove sediment from the shore. Examples of this biotope within areas which are moderately exposed to waves will not be as negatively affected by this pressure as sediment will be removed by wave action relatively quickly. Examples of this biotope which are in sheltered or very sheltered conditions sediment will be retained for longer, allowing greater negative effects to occur. Resistance and resilience have both been assessed as ‘Medium’. Overall the biotope has a ‘Medium’ sensitivity to smothering at the level of the benchmark.

Several studies found that increasing the vertical sediment burden negatively impact fucoids survival and associated communities. At the level of the benchmark (30 cm of fine material added to the seabed in a single event) smothering is likely to result in mortalities of understorey algae, invertebrate grazers and young (germling) fucoids. Resistance is assessed as ‘Low’ as all individuals exposed to siltation at the benchmark level are predicted to die. Once condition return to normal, recovery will be enable by vegetative growth from remaining Fucus tissue, resulting in a ‘Medium’ resilience. Overall the biotope has a ‘Medium’ sensitivity to siltation at the pressure benchmark.

Increased levels of diffuse irradiation correlate with increased growth in macroalgae (Aguilaria et al., 1999). Levels of diffuse irradiation increase in summer, and with a decrease in latitude. As Fucus vesiculosus is found in the middle its natural range in the British Isles an increase in the level of diffuse irradiation will not cause a negative impact on the species or the biotope. However, it is not clear how these findings may reflect changes in light levels from artificial sources, and whether observable changes would occur at the population level as a result. There is, therefore, 'No evidence' on which to base an assessment.

This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit propagule dispersal. But propagule dispersal is not considered under the pressure definition and benchmark.

Thompson & Schiel (2012) found that native fucoids show high resistance to invasions by the Japanese kelp Undaria pinnatifida. However cover of Fucus vesiculosus was inversely correlated with the cover of the invasive Sargassum muticum indicating competitive interaction between the two species (Stæhr et al., 2000). Stæhr et al. (2000) determined that the invasion of Sargassum muticum could affect local algal communities through competition mainly for light and space.

Hammann et al., (2013) found that in the Baltic Sea Gracilaria vermiculophylla could impact Fucus vesiculosus through direct competition for recourses, decreasing the half-life of germlings, and increasing the level of grazing pressure. To date Gracilaria vermiculophylla has only been recorded in Northern Ireland, and not on mainland Britain. The introduction of this species to intertidal rocky shores around the British Isles could have negative impacts on native fucoids, and could become relevant to this specific biotope.

Sensitivity assessment. Although evidence often indicates that invasive non-native species (INNS) can have a negative impact native species, no evidence can be found on the impacts of INNS on the characterizing species of this biotope. Evidence regarding other fucoids indicate that some mortality of characterizing species can occur through direct and indirect consequences of INNS being present. Due to the current lack of INNS which could cause a negative impact on this biotope resistance has been assessed as ‘High’ since invasive species have the potential to alter the recognizable biotope. Resilience has also been assessed as ‘High’. This assessment naturally leads to the conclusion that the biotope is ‘Not Sensitive’ to this pressure. However, return to ‘normal’ conditions is highly unlikely if an invasive species came to dominate the biotope. Indeed recovery would only be possible if the majority of the NIS were removed (through either natural or unnatural process) to allow the re-establishment of other species. Therefore actual resilience will be much lower (‘Low’ to ‘Very Low’).

Fucus vesiculosus is one of several harvested and exploited algal species. Seaweeds were collected from the middle of the 16th century for the iodine industry. Nowadays seaweeds are harvested for their alginates, which are used in the cosmetic and pharmaceutical industries, for agricultural supply, water treatment, and for human food and health supplements (Bixler & Porse, 2010). There is little information on the collection of Fucus spiralis. However if there is collection of this characteristic species the effects are likely to be very similar to that caused by the removal of Fucus vesiculosus.

The commercial harvest removes seaweed canopies which will have important effects on the wider ecosystem. Stagnol et al. (2013) investigated the effects of commercial harvesting of intertidal fucoids on ecosystem biodiversity and functioning. The study found that the removal of the macroalgae canopy affected the metabolic flux of the area. Flows from primary production and community respiration were lower on the impacted area as the removal of the canopy caused changes in temperature and humidity conditions. Suspension feeders were the most affected by the canopy removal as canopy-forming algae are crucial habitats for these species, most of them being sessile organisms. Other studies confirm that loss of canopy had both short and long-term consequences for benthic communities in terms of diversity resulting in shifts in community composition and a loss of ecosystem functioning such as primary productivity (Lilley & Schiel, 2006; Gollety et al., 2008). Due to the intolerance of macroalgae communities to human exploitation, the European Union put in place a framework to regulate the exploitation of algae establishing an organic label that implies that ‘harvest shall not cause any impact on ecosystems’ (no. 710/2009 and 834/2007).

Sensitivity assessment. The removal of Fucus vesiculosus canopy will significantly change the community composition of the biotope. The quantity of biomass removed from the shore and the regularity of removal will all affect how quickly the biotope will be able to recover. Fucus vesiculosus has a ‘Low’ resistance to removal as both of them are easy to locate and have no escape strategy. Resilience is ‘Medium’, however recovery will only be able to start when the pressure is removed from the shore i.e. harvesting is no longer occurring. A sensitivity of ‘Medium’ is recorded.

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures. The characterizing species Fucus vesiculosus creates a dominant turf within this biotope. The dominance of this characterizing species means it could easily be incidentally removed from this biotope as by-catch when other species are being targeted. The loss of this species and other associated species would decrease species richness and negatively impact on the ecosystem function.

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope. The resistance to removal is ‘low’ due to the easy accessibility of the biotopes location and the inability of these species to evade collection. The resilience is ‘Medium’, with recovery only being able to begin when the harvesting pressure is removed altogether. This gives an overall sensitivity score of ‘Medium’.

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